1. Field of the Invention
This invention relates to a method of forming an insulation film, using electric discharge, e.g. method of forming a passivation film by using sputtering.
2. Description of the Prior Art
Recently, in the field of semiconductor processing techniques, a method has come to be greatly needed which is adapted for forming a high-quality passivation film at low temperatures below 400.degree. C, for the surface stabilization of semiconductor elements fabricated of III-V group compound, for the insulative separation of metal wirings in the integrated circuit, and for the surface protection of semiconductor devices.
Among the methods for meeting such a requirement is a method of forming a passivation film by utilizing discharging phenomenon. According to this method, insulation films serving as various passivation films can be formed, with the temperature of the semiconductor substrate kept below 300.degree. C. In addition, the thickness of the formed film can be arbitrarily increased, having no upper limit and the grain of the film is very close so that high reliability can be attained. Therefore, this method is especially used, in the application to semiconductor fabricating techniques, when the uppermost passivation film is formed. For example, there is a method of forming a passivation film, using sputtering. In case of forming a film of Si0.sub.2 on a silicon substrate, there is used a fused quartz as a sputtering source. However, there is a drawback that the characteristics of the resultant elements are deteriorated due mainly to lattice defects caused in the vicinity of the Si-SiO.sub.2 interface by the surface injury in the sputtering process, to contaimination by Na ions introduced in the sputtering process, and to surface injury caused by impacts by electrons and ions during radio frequency sputtering. Accordingly, in case of bipolar IC's the h.sub.FE characteristics of the transistors are deteriorated while in case of MOS IC's the V.sub.th characteristics of the MOSFET's are lowered. It is thus not preferable to apply the method of forming a passivation film by sputtering, to semiconductor devices which requires high reliability, and especially to MOSIC's since in this case the ions accumulated in the gate electrode or in the gate insulation film often cause the V.sub.th characteristic of the MOSFET to be changed or deteriorated.